The Oregon Senate delivered a powerful message in support of tightening regulation on medical marijuana Wednesday by voting 29-1 for a bill aimed at curbing diversions to the black market.

Although the measure has drawn intense opposition among many patients and growers, lawmakers said that the success of the state’s new recreational pot market depends on getting a tighter handle on marijuana ostensibly grown for patients.

Sen. Ginny Burdick, D-Portland and chair of a House-Senate committee on implementing the marijuana legalization initiative passed by voters in November, said the large amount of marijuana diverted to the black market makes it harder for legal sellers to compete and could even threaten federal action against the state.

The state now produces an estimated $1 billion a year of “largely black market medical marijuana that ends up all over the country,” said Burdick, calling it a “problem which is far worse than I ever dreamed.”